Laser-induced breakdown spectroscopy for lambda quantification in a direct-injection engine

We apply laser-induced breakdown spectroscopy (LIBS) to determine local lambda values (i.e. the normalized air-fuel mass ratio) at the ignition location λip in a direct-injection single-cylinder optical research engine. The technique enables us to determine variations of λip for different fuel injection strategies, as well as correlations between variations in λip and the combustion dynamics. In particular we observe, that fluctuations in λip are not the major cause of cycle-to-cycle variations in the combustion process. Moreover, our experiments identify insufficient lean λip values as a source of misfires in lean combustions. In a combination of LIBS with laser-induced fluorescence (LIF), we obtain additionally information about the two-dimensional λ distribution. These results demonstrate the potential of LIBS to monitor λ values during mixture formation in gasoline engines.